Ohio State Researcher Team Invents Combined Solar Cell and Battery

Nanometer-sized rods of titanium dioxide (larger image) cover the surface of a piece of titanium gauze (inset). The holes in the gauze are approximately 200 micrometers across, allowing air to enter the battery while the rods gather light. Image Courtesy of Yiying Wu, The Ohio State University

A new technology developed by researchers at Ohio State University has the potential to increase the efficiency and decrease the cost of generating and storing the sun's energy. Led by professor of chemistry and biochemistry Yiying Wu, the team has created a combined solar cell and lithium storage battery with an efficiency of electron transfer between the two components of almost 100%, in a design which they believe will reduce costs by up to 25%.

“The state of the art is to use a solar panel to capture the light, and then use a cheap battery to store the energy,” Wu said. “We’ve integrated both functions into one device. Any time you can do that, you reduce cost.”

The design builds on the team's previous development of the KAir battery, an open-air battery which stores energy by reacting with oxygen in the air, which won the $100,000 clean energy prize from the U.S. Department of Energy earlier this year. “Basically, it’s a breathing battery,” Wu said. “It breathes in air when it discharges, and breathes out when it charges.” The new development adds a titanium gauze, which captures sunlight and converts it into electricity, while still allowing air to pass through for the battery to work.

To make this titanium mesh work as a solar cell, it needed to be tuned to collect the right wavelengths of light. This was achieved by dying the mesh to a reddish color; after testing a range of dyes, the team eventually settled on iron oxide - in other words, rust.

The result is a three-layered component, consisting of a rust-coated titanium gauze separated from the lithium plate battery by a thin layer of porous carbon. Because the energy is generated just fractions of a millimeter from the battery, almost all of the energy generated is stored, compared to around 80% for a conventional solar panel connected to a battery with wires.